This invention relates to electromedical apparatus and particularly to implantable, transvenous catheter-type electrode devices. The apparatus of this invention is particularly useful for cardiac defibrillation in conjunction with an implantable cardioverter/defibrillator (ICD).
Defibrillating the human heart is accomplished by applying an electrical waveform to the cardiac muscle with appropriate electrodes, causing the cessation of the rapid uncoordinated contractions of the heart (fibrillation), and a restoration of normal beating of the heart. In the past, various electrode devices and/or methods have been used and proposed for defibrillation. However, these devices are generally complex, difficult to construct and utilize, and are inefficient to use.
A well-functioning, unitary defibrillation electrode catheter should accomplish three functions. The first is that it should provide a high surface area, low impedance current path for the high energy defibrillation pulse, which may be up to 750 volts. Secondly, it should provide a pair of pacing electrodes which have a small surface area to also deliver a low energy pacing pulse of approximately 5 volts. The small surface area is desired so that pacing may be accomplished at a high local current density resulting in lower overall energy usage. The low energy usage of the pacing function is of concern since pacing may be required to proceed uninterrupted for many years. The third function of the defibrillation electrode is sensing. A pair of small surface area electrodes, commonly referred to in the art as a bipolar pair, is used to sense a local differential voltage representing the electrogram in the ventricle of the heart. Ideally, the bipolar pair of electrodes additionally serve as pacing electrodes.
Besides providing for the above three basic functions, the unitary electrode lead must also prevent possible detrimental interactions. Thus, the electrode lead must keep the pacing pulse from being shunted by the defibrillation electrodes. The electrode catheter must also keep the sensed electrocardiographic signals from being corrupted by signals from the large defibrillation electrodes. Finally, the electrode lead must keep high defibrillation currents from flowing through the smaller pacing and sensing electrodes which could polarize them and interfere with their ability to properly sense the electrogram after a defibrillation pulse.
The current state of the art includes electrode apparatus having four separate electrodes, distally disposed, each linked to a separate conductor or lead, and each of which runs the length of the apparatus to a proximal connection end. Both co-axial and multi-lumen configurations of such leads exist. However, all of such four lead configurations present limitations in terms of minimizing apparatus diameter or profile. And, since such large apparatus are used intravascularly in human beings, this limitation is critical.
Despite the need for a electrode apparatus which overcomes the limitations and problems of the prior art, none insofar as is known has been proposed or developed. Accordingly, it is an object of the present invention to provide an apparatus which overcomes the limitations and short comings of the prior art. Particularly, it is an object of the present invention to provide an improved transvenous defibrillation catheter apparatus which is safe, reliable, and inexpensive to manufacture. A further object of this invention is to provide a low profile, minimal diameter electrode apparatus. Yet another object of this invention is to provide a full function defibrillation electrode apparatus which utilizes not more than three, and preferably two conductive leads. A final object of this invention is to provide and electrode apparatus in which lead conductor requirements are minimized by solid state multiplexing which is accomplished at the distal end of the apparatus.